Clear brine fluids are solids-free, industrial fluids widely used in operations where control of pressure in a well is needed, such as in the oil and gas industry, and play an important role in oil exploration and development of deep water wells, high-pressure and deep oil wells, oil sands, and the like. Clear brine fluids find use in well completion, work-over, drilling and fracturing operations, and serve a variety of functions such as a displacement fluid to remove drilling muds, as drill-in fluids, as permanent packer fluid. They inhibit undesirable formation reactions such as clay swelling and are used in preparing well equipment for production, e.g., during insertion of liners, screens, packers, and other equipment.
Clear brine fluids can be prepared with a variety of salts, generally halide salts, at various concentrations to provide specific densities for particular applications. For example, brines with densities ranging, e.g., from 8.4 to over 22 lbs/gal (ppg), may be desired. Commonly used salts include chloride and bromide salts of sodium, potassium, calcium and zinc. Ammonium salts, iodine salts, and other metals have also been used. More than one salt may be present in the fluid.
Bromide fluids, e.g., sodium, potassium and calcium bromide brines, are high density clear brine fluids that are suitable for deepwater production and high temperature/high pressure oil and gas formations. For example, bromide fluids are used in deepwater fracturing operations in order to provide the necessary pressure in the well to successfully fracture the geological formation area that supplies oil and gas to the wellbore allowing for higher volume flows to the production piping.
Clear brine fluids are solids free and thus contain no particles that might plug or damage a producing well or equipment and are used over a wide temperature range. The amount of a particular salt in a brine fluid, and thus the density of the brine, is limited by the solubility of that salt in water. Precipitation of the salt during use must be avoided, and many salts cannot be used on their own in higher density solutions, e.g., 12 ppg or 14 ppg to 20 ppg. Historically, the need for high density clear brine fluids, e.g., >14.2 ppg, has been met by using zinc bromide to blend up calcium bromide to higher densities. Zinc bromide and cesium formate brines traditionally have been used to achieve higher density in completion fluids, up to 19 ppg for high pressure applications such as kill-fluid and on-the-shelf gas wells (high temperature/high pressure).
However, zinc based fluids have environmental and economic limitations. Zinc is regulated and not environmentally friendly and requires a zero-discharge system when in use. Zinc contaminated flow-back and well-produced water has to be collected and shipped to shore for disposal or treatment and cannot, e.g., be pumped off-rig into the Gulf of Mexico. These regulations and a growing consciousness regarding the contamination of ground water has increased the interest in new clear brine fluids that are more environmentally friendly and do not require zero-discharge. A clear brine fluid is needed that can provide high densities and low crystallization temperatures without using zinc components, which fluids can be used in applications typically served with the present zinc containing fluids such as zinc/calcium bromide brines.
However, it has been found that certain crystallization suppressant additives that provide a thermally stable, environmentally acceptable, high density brine, can also cause an unacceptable increase in viscosity of the brine. This may prevent the brine from being used in many applications. A crystallization suppressant product is still needed that will provide high density brines, e.g., 12 ppg or 14 ppg to 20 ppg, with acceptably low viscosity.